1. Field of the Invention
The present invention relates generally to a method for generating a test signal for testing the accuracy of the Carrier to Interference plus Noise Ratio (CINR) measurement of a subscriber station through a base station emulator, and, more particularly, to a method for generating a test signal for testing the accuracy of the CINR measurement of a subscriber station, which is capable of efficiently and simply testing the accuracy of CINR measurement using a single base station emulator.
2. Description of the Related Art
Currently, methods of wirelessly accessing the Internet include a method for accessing the Internet via a mobile telephone network based on a Wireless Application Protocol (WAP) or Wireless Internet Platform for Interoperability (WIPI) platform, and a method for accessing the Internet via a public wireless Local Area Network (LAN) or an Access Point (AP). However, the method using a mobile telephone network has fundamental limitations on the use thereof as a universal Internet access method due to the limited screen size, the limited input interface, and the measured rate-based billing system. Meanwhile, the method using a wireless LAN has fundamental problems in that it can only be used within a range having a radius of tens of meters around an AP, and in that it also has poor mobility. In order to overcome such problems, ‘portable Internet service’ (mobile WiMAX, or WiBro, which is a subset of mobile WiMAX, and a Korean portable Internet standard) has been proposed as wireless Internet service capable of enabling high-speed Internet access at ADSL-level quality and cost, either when at rest or in intermediate-speed motion.
Meanwhile, a performance test of a subscriber station is a series of low-quality product filtering processes of, prior to marketing and sales, identifying subscriber stations exhibiting erroneous operation and deteriorated performance in advance and preventing the subscriber stations from being distributed on the market. In Korea, the law requires that the Korean Telecommunications Technology Association (TTA) establish a performance test procedure for information & communication equipment, and that information & communication equipment that does not pass the test be prohibited from being distributed on the market. Efforts to establish a test performance procedure for subscriber stations in the portable Internet, which is attracting attention as a new wireless communication system, have been made.
‘CINR’, which is one of the items of such a performance test, is an abbreviation for ‘Carrier to Interference plus Noise Ratio,’ and refers to a value that is obtained by dividing the power value of a signal carrier (hereinafter referred to as a ‘desired signal’) by the power value of the sum of an interference signal and a noise signal. That is, since the case where CINR is relatively high corresponds to the case where a desired signal is stronger than noise and interference, higher-quality signals can be received, so that the probability of receiving data without error increases. In contrast, when CINR is relatively low, the probability of receiving data mixed with errors due to noise and interference increases, thereby deteriorating service quality. A portable Internet system makes subscriber stations report CINR in consideration of the fact that the data error rate varies with CINR, and manages the subscriber stations based on the information. A ‘CINR measurement accuracy test procedure’ is a test for determining whether a subscriber station accurately reports CINR, and is a test procedure essentially required for the establishment of an environment in which a base station can acquire accurate CINR information and manage subscriber stations. In generally, in a ‘CINR measurement accuracy test’, CINR reported by a subscriber station is compared with the CINR for a signal actually provided to the subscriber station for measurement, and the subscriber station is considered to be a subscriber station having no abnormality if the difference therebetween is equal to or less than a predetermined reference value.
FIG. 1 is a system configuration diagram illustrating a method for generating a test signal for testing the accuracy of the CINR measurement of a subscriber station in a portable Internet system according to an example of the prior art, and illustrates a method for generating a test signal using two or more signal generators. According to the measuring system shown in FIG. 1, CINR is adjusted to a desired value by manually controlling the power ratio of signals respectively generated and output from two signal generators 10 and 20, with a signal, generated and output from one signal generator 10, being considered to be a desired signal desired by a portable subscriber station 100, and with a signal, generated and output from the other signal generator 20, being considered to be an interference signal. Of course, the two signals are the signals of different pieces of data.
However, in the case where a test is performed using the measuring system shown in FIG. 1, two or more signal generators 10 and 20 are required, so that both devices must be manipulated so as to adjust the CINR, a trigger line 50 for maintaining synchronization must be connected between the signal generators 10 and 20 so as to cause signal transmission time points to coincide with each other, and a combiner must be employed so as to mix the signals generated and output from the signal generators 10 and 20 and send the resulting signal to the subscriber station 100, with the result that there arise problems of inconvenience and low efficiency. Furthermore, according to the measuring system, a network entry process cannot be performed on the subscriber station 100, so that there arises a problem in that whether the network entry process of the subscriber station 100 and a report on the accuracy of later CINR measurement are accurate cannot be checked.
FIG. 2 is a system configuration diagram illustrating a method for generating a test signal for testing the accuracy of the CINR measurement of a subscriber station in a portable Internet system according to another example of the prior art, and illustrates a method for generating test signals using one base station emulator 60 and one signal generator 70. Here, the base station emulator 60 is a portable Internet measuring instrument that acts as a substitute for an actual base station by receiving signals sent by a portable subscriber station 100 to access a base station and sending corresponding signals, and that has a function of measuring the performance of the subscriber station 100. As described above, in the system shown in FIG. 2, the subscriber station 100 can go through a network entry process through the base station emulator 60, in which case the signal generator 70 performs a function of generating an interference signal, and can adjust CINR using the power ratio of a desired signal, output from the base station emulator 60, and an interference signal, output from the signal generator 70. In the case where a test is conducted using this method, there is an advantage in that whether a CINR report made after network entry is accurate can be determined, which is impossible using the first method. If the CINR measurement accuracy test procedure is configured to test CINR reports made after the network entry of the subscriber station 100, tests can be conducted using only the second system.
However, since this case requires two devices also, there are problems in that a trigger line 90 is required for synchronization between the transmission time points of a station's signal and an interference signal, and two signals must be mixed with each other using a combiner 80 and then be sent to the subscriber station 40 for connection to the subscriber station 40. Moreover, since both devices must be manipulated so as to adjust CINR, there are problems of low manipulation efficiency and inconvenience.